SEC FORM 4

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person^*

Cook D. Andrew

(Last)

(First)

(Middle)

C/O ALTERRA CAPITAL HOLDINGS LIMITED

ALTERRA HOUSE, 2 FRONT STREET

(Street)

HAMILTON, BERMUDA

HM 11

(City)

(State)

(Zip)

2. Issuer Name and Ticker or Trading Symbol
ALTERRA CAPITAL HOLDINGS Ltd [ ALTE ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director	10% Owner
X	Officer (give title below)	Other (specify below)
	EVP, Business Development

3. Date of Earliest Transaction (Month/Day/Year)
05/01/2013

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Common Shares	04/01/2013		M		18,077	A	$26.48⁽¹⁾	253,037	D
Common Shares	05/01/2013		F		14,706	D	$32.55⁽¹⁾	238,331	D
Common Shares	05/01/2013		D		167,066	D	⁽²⁾	71,265	D
Common Shares	05/01/2013		D		71,265	D	⁽³⁾	0	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
Warrant (right to buy shares)	$26.48⁽¹⁾	05/01/2013		M			18,077	⁽⁵⁾	05/15/2016	Common Shares	18,077	$0	0	D
Options (right to buy shares)	$26.48	05/01/2013		D			113,307	⁽⁶⁾	09/01/2016	Common Shares	113,307	⁽⁴⁾	0	D

Explanation of Responses:

1. Warrants exercised pursuant to a cashless exercise in which 14,706 shares were withheld to pay the exercise price based on a per share price of $32.55, which equaled the last reported sale price for the common shares of Alterra Capital Holdings Limited (the "Issuer") as reported on NASDAQ Global Select Market on April 30, 2013. Cash was paid in lieu of fractional shares of the Issuer in the cashless exercise based on the average (weighted by daily trading volume) of the last reported price for the Issuer on NASDAQ Global Select Market for each of the 20 consecutive trading days immediately prior to the exercise of the warrant. In addition, the Issuer paid out certain accrued dividends in cash upon the exercise of the warrants.

2. Disposed of pursuant to the Agreement and Plan of Merger, dated as of December 18, 2012 (the "Merger Agreement") between the Issuer, Markel Corporation ("Markel") and Commonwealth Merger Subsidiary Limited in exchange on a per share basis for (i) the amount of shares of Markel common stock equal to the number of shares of Issuer common stock multiplied by 0.04315 plus (ii) $10.00 in cash, without interest, together with any cash paid in lieu of fractional shares relating to each award and form of ownership.

3. Restricted stock of the Issuer that did not automatically vest upon the closing of the transactions contemplated by the Merger Agreement (the "Closing") disposed of pursuant to the Merger Agreement in exchange on a per share basis for the amount of shares of Markel restricted stock equal to the number of shares of Issuer restricted stock multiplied by the Incentive Exchange Ratio, together with any cash paid in lieu of fractional shares. The Incentive Exchange Ratio is (i) 0.04315 plus (ii) (a) $10.00 divided by (b) the volume weighted average share price per share of Markel common stock for the five consecutive trading days immediately preceding the second trading day before the closing date.

4. Disposed of pursuant to the Merger Agreement in exchange for options exercisable for shares of Markel common stock (equal in number to the number of shares of Issuer common stock subject to the options multiplied by the Incentive Exchange Ratio) at an exercise price equal to the exercise price as of immediately prior to the Closing divided by the Incentive Exchange Ratio, together with any cash paid in lieu of fractional shares.

5. Warrant is immediately exercisable.

6. All options are currently exercisable.

Remarks:

	Matthew Crusey, Attorney-In-Fact	05/03/2013
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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